1. Field of the Invention
The present invention relates to a resin-sealed semiconductor device and a lead frame used in a resin-sealed semiconductor device.
2. Description of the Related Art
A resin-sealed semiconductor device, such as an IC or LSI, is formed through a dicing step for separating semiconductor chips arranged on a wafer, independently from one another, a die bonding step for mounting a separated semiconductor chip on a lead frame, a wire bonding step for connecting an electrode pad on a semiconductor chip with an inner lead of the lead frame through a wire, such as an Au or Al wire, and a packaging step for resin-sealing the semiconductor chip and the wire and the inner lead connected thereto.
In general, the transfer molding method or the potting method is used to resin-seal a semiconductor chip.
FIG. 1 is a partially cross-sectional view of a conventional resin-sealed package, in which a semiconductor element is coated with resin. A conventional resin-sealed semiconductor will be described with reference to FIG. 1.
A semiconductor chip 1, on which an integrated circuit and the like are formed, is bonded to a die pad 21 of a lead frame 2 with adhesive.
A plurality of inner leads 22 are arranged such that their distal ends are opposed to the semiconductor chip 1 with a space. The distal ends of the inner leads 22 are connected to an electrode pad (not shown) formed on the main surface of the semiconductor chip 1 through a bonding wire 3, such as an Au or Al wire.
The semiconductor chip 1, the die pad 21, the bonding wire 3 and the inner leads 22 are sealed with a resin sealing material 4, such as an epoxy resin 4. The unprocessed lead frame 2, on which the semiconductor chip 1 is mounted, is subjected to the resin sealing process. After the lead frame is resin-sealed, an outer lead portion (a portion outside the package (not shown)) of the lead frame is subjected to a forming process. A resin-sealed semiconductor device is thus completed.
A lead frame is generally about 150 .mu.m thick, and can be as thin as 100 .mu.m. The lead frame is made of an Cu alloy or an Fe-42Ni alloy. A semiconductor chip, particularly a silicon chip, is generally about 350 .mu.m thick and it has been attempted to reduce the thickness of a chip to 150 to 200 .mu.m.
The surface of the semiconductor chip 1 is generally coated with a passivation film, such as PSG (Phosphosilicate Glass), Si.sub.3 N.sub.4 or polyimide.
FIG. 2 is a cross-sectional view showing a conventional thin resin-sealed package.
In FIG. 2, the die pad 21 of the lead frame 2 shown in FIG. 1 is omitted. Side surfaces of a semiconductor chip 1 is adhered to a lead frame 2 with insulating adhesive (not shown).
A plurality of inner leads 22 are arranged such that distal ends thereof are opposed to the semiconductor chip 1 with a space. The distal ends of the inner leads 22 are connected to an electrode pad (not shown) formed on the main surface of the semiconductor chip 1 through a bonding wire 3, such as an Au or Al wire.
The semiconductor chip 1, the bonding wire 3 and the inner leads 22 are sealed with a resin sealing material 4, such as an epoxy resin 4.
FIG. 3 is a cross-sectional view showing another conventional thin resin-sealed package.
A lead is formed by means of a TAB (Tape Automated Bonding) method without using a lead frame.
As regards a TAB lead 5, an inner lead 51 is supported by a polyimide film 6. The distal end of the inner lead 51 of the TAB lead 5 on the polyimide film 6 is connected to a semiconductor chip 1 via a bump (projection electrode) 7 formed on a connection electrode (pad electrode (not shown)).
The semiconductor chip 1, the inner lead 51 and the polyimide film 6 are sealed with a resin sealing material 4, such as an epoxy resin 4.
To reduce the thickness of the conventional resin-sealed package as shown in FIG. 1, the die pad portion of the lead frame 2 is omitted as shown in FIG. 2, or the TAB method is employed as shown in FIG. 3.
When the TAB method is used, it is easy to form a thin resin-sealed package; however, this method itself is expensive. In addition, since a TAB lead is very thin, the outer lead portion (the portion outside the package) is very weak, and problems such as lead bending or lead breakage arise. When the die pad is omitted as shown in FIG. 2 to reduce the thickness of the semiconductor device, if the device is too thin, a bonding wire may be exposed to the outside of the package. Moreover, when the semiconductor chip becomes thinner, the strength of the chip itself it considerably reduced, so that a crack is liable to occur.
Further, to reduce the thickness of the resin-sealed package, reduction of the thickness of the die pad itself has been proposed. However, even if the die pad is thinned, the thickness of the semiconductor chip is not reduced very much and the mechanical strength thereof is lowered. Therefore, it is difficult to hold the semiconductor chip stably.